How to use the sprayer calibration calculator
- Choose US units (gallons, mph, inches) or metric units (liters, km/h, meters).
- Enter the flow per nozzle that you measured by catching the output for a minute, the travel speed and the nozzle spacing.
- Optionally enter the area to spray and the tank size.
- Read the application rate in both unit systems, the spray needed for the area, the area covered by one tank and the number of tanks.
Formula
US: gallons per acre = 5940 x gallons per minute per nozzle / (mph x nozzle spacing in inches)
Metric: liters per hectare = 600 x liters per minute per nozzle / (km/h x nozzle spacing in meters)
Spray needed = application rate x area
Area per tank = tank size / application rate, and tanks needed = spray needed / tank size
The constants 5940 and 600 convert the units of flow, speed and spacing into gallons per acre and liters per hectare. The application rate is the same whichever system you use.
0.42 gpm per nozzle at 5.5 mph with 30 inch spacing
The application rate is 5940 x 0.42 / (5.5 x 30) = 15.12 gallons per acre, which is 141.43 liters per hectare. Spraying 20 acres needs 15.12 x 20 = 302.4 gallons.
A 300 gallon tank covers 300 / 15.12 = 19.841 acres, so 20 acres needs 1.008 tanks. That is just over one tank, so fill a little extra or plan a second partial load.
Calibrating the sprayer
Measure the output of each nozzle for a fixed time at your working pressure, and check that they agree. A worn nozzle can put out noticeably more than a new one. Then measure the speed by driving a known distance with the sprayer on, because the speed on a dashboard is not always accurate.
Follow the product label for the rate to use. The page only works out the rate your sprayer delivers. For a lawn product, see the lawn fertilizer calculator, and for the travel speed check the average speed calculator.
Changing the rate
To apply more per acre, slow down, use a larger nozzle or raise the pressure. Doubling the speed halves the rate. Raising the pressure increases the flow only by the square root, so a fourfold pressure increase doubles the flow. Rerun the page after any change.
To plan the water flow for a sprinkler system rather than a sprayer, use the irrigation zone flow calculator.
Assumptions and limits
- All nozzles put out the same flow and are spaced evenly along the boom.
- The speed stays constant over the field, including at the turns, which are ignored.
- The tank is filled to the size you enter and is emptied completely.
- Product rates and mixing instructions come from the label. This page does not give them.
Frequently asked questions
How do I calibrate a boom sprayer?
Catch the output of each nozzle for a minute, measure your travel speed over a known distance, then use the page to turn the flow, speed and spacing into gallons per acre.
What is nozzle spacing?
It is the distance between neighboring nozzles on the boom. In US units it is in inches, and in metric units it is in meters.
Why does the page ask for flow in gallons per minute?
That is how nozzle output is measured and rated. Convert from ounces per minute by dividing by 128 if you measured in ounces.
How many tanks will I need?
The page divides the spray needed by the tank size. A result a little above a whole number means a small extra load.